According to this study:
* Weight loss in premenopausal women was greater on a lowcarbohydrate diet.
* Weight-related metabolic risk factors improved more on a lowcarbohydrate diet.
* Mean one-year weight loss for all diets was modest.
In a yearlong comparison of four weight-loss programs with varying levels of carbohydrate intake, a low-carbohydrate diet led to greater weight loss and more favorable metabolic effects in premenopausal overweight or obese women.
The study compared Atkins, a very low carbohydrate diet; Zone, a low-carbohydrate diet; Ornish, a very high carbohydrate diet; and LEARN (Lifestyle, Exercise, Attitudes, Relationships, and Nutrition), a low-fat, high-carbohydrate diet based on national guidelines. The primary outcome measure was weight loss.
Premenopausal women ages 25 to 50 years having a stable body mass index (BMI) of between 27 and 40 were eligible to participate. Three hundred and eleven participants were randomized to one of the four diets and given a book describing it. One registered dietitian taught all four groups about their diet in eight weekly one-hour group classes. Behavior modification techniques were also discussed. Each group was given specific dietary targets, such as limiting their carbohydrate intake to a certain number of grams per day.
Data were collected at baseline and at two, six, and 12 months. Participants reported their dietary intake and energy expenditure by phone. Weight, height, waist and hip circumference, and body fat percentage were also measured. Metabolic measures included cholesterol, triglycerides, insulin, glucose, and blood pressure.
At 12 months, the mean weight losses in the Atkins, Zone, LEARN, and Ornish groups were 4.7, 1.6, 2.2, and 2.6 kilograms, respectively. At two and six months, weight loss in the Atkins group was significantly greater than for all other groups; weight loss did not differ significantly among the other three diets. Changes in BMI, body fat percentage, and waist-hip ratio were in line with weight loss. Blood samples taken at baseline and at two, six, and 12 months were analyzed for 84% of participants. High-density lipoprotein and triglyceride levels significantly favored the Atkins group. Changes in low-density lipoprotein levels, which favored the Ornish and LEARN diets at two months, were not significantly different among the groups at six and 12 months. Atkins group members had the greatest decrease in mean systolic and diastolic blood pressures at all time points, and the decrease in systolic pressure was significantly greater in that group at 12 months. Insulin and glucose levels were comparable among groups at all time points.
The authors conclude that at one year, greater weight loss and more favorable metabolic outcomes were achieved with the Atkins diet than with the other three diets and that its effects on lipid profiles were not of immediate concern. However, they note that it was unclear whether it was the diet's low-carbohydrate content or another aspect that conferred these benefits.